ENK5-2000-00313 The influence of tar composition and concentration on fouling, emission and efficiency of micro and small scale gas turbines by combustion of biomass derived low calorific valued gas

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EESD (Energy, Environment and Sustainable Development) : Electricity : Thermochemical Conversion

Proposal No:	ENK5-2000-00313
Date Prepared:	February 2004
Source:	European Bio-Energy Projects (EUR 20808)

Introduction

Biomass, if properly grown and managed, is a renewable resource and an attractive feedstock for gasification processes, which produce a gas rich in carbon monoxide and hydrogen. Unfortunately, a small fraction of the biomass is converted to tar. Tar will impose serious limitations on the use of the produced low calorific fuel (LCV) gas due to the fouling of downstream process equipment and emission of carbon monoxide. For future advanced biomassbased power systems these processes must be further developed, in particular in biomass fired integrated small-scale gasifiers and gas turbine systems

Future biomass-based power-generation technologies have to provide a higher efficiency at lower costs by combining well-established gasification processes, sophisticated low calorific value gas cleaning and reliable combustion with minimal emissions. For this reason fuel upgrading, combustion and cycle improvement and lower emission are required. The innovation aimed at in this project is to research the different gas cleaning steps and determine how much gas cleaning is required to deliver to the gas turbine section a fuel gas which will not foul and which can be combusted with low emissions.

Activities

The work is based on seven work packages. The first deals with coordination. In the second work-package research is performed to improve tar measurements and measurement techniques that are used within the project. For this a novel on-line total tar analysing method is used in combination with identification of tar components with a solid phase absorption technique.

The fourth work package contains experiments with advanced set-ups of state-of-the-art fixed bed gasifiers, gas cleaning and tar removal by low temperature techniques such as filters, scrubbers and catalytic crackers.

In parallel the fifth work package researches pressurised gasification in combination with high temperature gas cleaning by ceramic filters. The third work package concentrates on experimental tar fouling testing and modelling of a fuel gas compressor designed for the operation on biomass derived low calorific value fuel gas. In parallel with the fifth work package, a combustor design is made based on measurements performed with a gas turbine combustor operated on real LCV gas and two combustors operated on simulated LCV gas. This new combustor will be applied in the micro gas turbine experiments.

In the sixth work package the fuel gas compressor and micro turbine on simulated LCV gas are experimentally tested. All work will be carried out in close relation to industry, who will use their expertise to assure the technical and economical implementation of project results in future plant designs, aspects of which will be the central theme of the final seventh work package.

Results

In the two years of the TARGeT project, two tar measurement techniques were enhanced and compared during on-site tests. These techniques were the on-line GC-FID-FID technique and the offline S.P.A technique. In combination, these techniques show that good tar analyses of biomass derived fuel gas is possible and accurate.

The methods were used to measure tars inside the integrated systems of a 1 MW Pressurised Fluidised Bed Gasifier (PFBG) with ceramic filter system and gas turbine combustor and the integrated system of a 1 MW Downdraft Fixed Bed gasifier with sawdust filters, scrubber and fuel gas compressor.

Tests show that tars can slip through the gas cleaning system. This fuel gas compressor will be used to supply the required amount of pressurised fuel gas to a small-scale turbine with LCV gas combustor.

Compression tests with LCV gas were performed and changes to the gas cleaning and compressor were made to decrease tar condensation inside the compressor. These tests show promising results for further integration of the gas turbine. The high temperature gas cleaning with filters of b-cordierite operated at 800°C showed high dust removal efficiencies, no tar clogging and small influences in tar cracking. These types of gas cleaning are considered as very useful in Biomass Fired Integrated Small-scale Gasifiers and Gas Turbine Systems.

A new combustor was designed and constructed with a thermal input of 500 kW at 3.3 bar to fit the small-scale turbine. Combustion chamber modelling for the first burner and modelling for the second burner are performed together with modelling of emissions from tar containing LCV gas.

Impact and exploitation

The active involvement of all the participants has brought both academic and industrial knowledge into the project. The skills to solve the scientific and technical problems related to thermal conversion of biomass/renewable solid fuels, gas cleaning and gas analyses have proven that clear progress in power production from biomass is possible. In the last year of the project more work will be performed on a complete integrated system.